Silicon on insulator (SOI) semiconductor devices are increasingly utilized. A SOI semiconductor device includes a semiconductor substrate, or bulk silicon. On the semiconductor substrate is an insulating layer, typically silicon dioxide. The insulating layer is known as the box layer. On the box layer is a silicon region, termed the body, that is typically p-doped. The source and/or drain junctions, shallow trench isolation (STI) regions, gate stacks, spacers and other structures, are formed on the silicon. Conductive structures, such as interconnects and contacts, electrically connect devices within the SOI semiconductor device. Typically, the contacts are formed of tungsten, while the interconnects are composed of copper.
SOI semiconductor devices may have failures, such as shorts or open circuits, that arise when the semiconductor device is fabricated. Similarly, components of the semiconductor devices may fail during testing and/or operation. As a result, it is desirable to perform failure analysis to determine the type of failure that has occurred, the components affected and the location of the failure. Additionally, analysis of the structural features of the device may provide information on fabrication process parameters and control.
One method analyzing semiconductor devices is passive voltage contrast. In the passive voltage contrast technique, a scanning electron microscope (SEM) may direct an energetic beam of electrons to an integrated circuit or wafer placed on a stage in a vacuum chamber. Upon directing electrons onto the test circuit or wafer, secondary electrons may be produced. This technique has typically be used for detecting defects, such as a gate oxide breakdown from the front side of the device. The secondary electrons may be emitted when there is a conductive path for electrons to flow. Consequently, the image of areas where there is a conductive path may be brighter than the areas in which there is no conductive path. By determining if the area around the gate oxide region is dark or bright, breakdown in gate oxide region may be detected. If the gate oxide has broken down, the area will appear bright since a conductive path has been formed from the gate to the channel. Conversely, a sound gate oxide region will appear dark.
Structures within the body of the device may similarly exhibit such variation in the emission of secondary electrons and the resulting image contrast when illuminated by an energetic charged particle (electron or ion) beam. For example, the secondary emission from p-type regions and n-type regions typically is different. Thus, voltage contrast techniques may be advantageously applied to inspect structures within the semiconductor body. However, an energetic particle beam, such as an SEM beam directed to the topside of the chip cannot penetrate to these structures.
Accordingly, there is a need in the art for techniques for backside voltage contrast inspection of semiconductor devices.